The present invention relates to a separating material, a novel method for producing the same, and the use of the separating material in several separating applications.
By separating material it is meant a material that is useful as an adsorption material and/or as a dialysis material and/or as a filtration material for the separation of substances, having specific chemical or physical properties, or substances, being recognized by specific recognition compounds, from a fluid, especially a liquid. Separating materials in the sense of the present invention are particularly useful in the separation or depletion, respectively, of undesired substances from liquids, e. g. the adsorptive separation of toxins from blood plasma.
Separating materials for adsorptive separation applications generally comprise a solid phase substrate material or matrix material, respectively, which carries on its surface active sites for the more or less specific adsorption of compounds having particular properties, e. g. positive or negative charges, specific chemical structures or functional groups etc. The solid phase substrate material may often be a porous or non-porous polymer having functional surface groups or chains of a graft copolymer being functionalized and being formed by graft polymerization of monomers onto the surface of the polymeric matrix material.
The U.S. Pat. No. 5,556,708 describes a method for the production of an adsorption material by graft polymerization of a nitrogen-containing polymer with an ethylenically unsaturated monomer in an aqueous environment in the presence of two reactants, said two reactants consisting of carbon tetrachloride and a reducing agent, selected from sodium dithionite, rongalite, hydrazine, and ascorbic acid. According to the description and the examples of U.S. Pat. No. 5,556,708, sodium dithionite seems to be the only one reducing agent that had been tested. Also, even though it is claimed that the nitrogen-containing polymer may be selected from polyamides, polysulfonamides, polyurethanes, and polymers having primary and secondary amine groups in a side chain, only a polyamide membrane, particularly a nylon 6,6 membrane, had been tested in the examples as the nitrogen-containing polymer. U.S. Pat. No. 5,556,708 leaves unclear whether and how the method may work with a nitrogen-containing polymer having primary and secondary amine groups. It is known that amides form radicals with the reducing agents used according to U.S. Pat. No. 5,556,708, but there is no mechanistical explanation how the graft polymerization should work with primary and secondary amines.
One major disadvantage of the method of U.S. Pat. No. 5,556,708 is the prescribed use of an organic reactant, especially of carbon tetrachloride in the graft polymerization process. Even if the produced material is thoroughly cleaned after the production process, there will still be amounts of carbon tetrachloride remaining in the porous polymeric structure. The toxicity of carbon tetrachloride thus makes the produced adsorption material inappropriate for medical applications, as e. g. the adsorption of toxins from blood or in hemodialysis. On the other hand, the more or less complete removal of carbon tetrachloride from the adsorption material of U.S. Pat. No. 5,556,708 by exhaustive rinsing or washing of the material would cause enormous costs and would make the material commercially unattractive.
Summarizing, disadvantages of prior art separating materials include the following: the substrate materials are not biocompatible or blood compatible, thus the materials are not useful for medical applications; the reactions to produce such separating materials require organic solvents which are toxic or biohazardous, thus the materials are not useful for medical applications; the reaction conditions to produce such separating materials are often harsh in a way that the preparation methods are restricted to reactants which withstand such conditions; and the reactions to produce such separating materials, if UV activation is used, do not provide for a uniform functionalization over the entire surface of a porous polymeric matrix.